Social behavioural profile of cocaine in isolated and grouped male mice

Studies concerning the relationship between cocaine and aggression in humans as well as in animals have discrepant outcomes. Increases, decreases, or no changes, have been reported after single or chronic cocaine administration in animal models. To clarify, at least in part, the complex behavioural actions of cocaine, the present study evaluated cocaine effects on social behaviours of mice exposed to different situations (isolated or group housed) using confrontations between two male mice in a neutral area. Different doses of cocaine (6, 25 and 50 mg/kg) were administered in a single or binge pattern (three doses in 24 h) and the behavioural test was performed 20 min after the last injection. No increases in aggression were observed in any situation tested. Instead, cocaine at the two higher doses employed (either in single or binge administration), decreased aggressive behaviours in isolated mice, with no changes being observed in grouped animals. In both types of animals, cocaine increased defensive elements (avoidance/flee) and abolishes social contacts. In conclusion, cocaine presents an anti-aggressive action and may be interpreted as having an anxiogenic-like effect.     

Attenuation of cocaine-induced conditioned locomotion is associated with altered expression of hippocampal glutamate receptors in mice lacking LPA1 receptors

Rationale

Lysophosphatidic acid is a phospholipid mediator that modulates neurodevelopment and neurogenesis in the hippocampus through its actions on LPA1 receptors. Emerging evidences support LPA₁ as a mediator of learning and emotional behaviour. There are no studies addressing its role on behaviours associated to drug abuse.

Objectives

We examined whether genetic deletion of LPA1 receptor in maLPA₁-null mice affected either cocaine-induced conditioned locomotion (CL) or behavioural sensitization (BS) induced by repeated cocaine exposure. We also analysed whether cocaine induced changes in the expression of functional markers of both dopamine- and glutamate-related genes in the striatum and the dorsal hippocampus.

Methods

We monitored cocaine-induced CL and BS in both genotypes of mice. Striatal dopamine and hippocampal glutamate-related genes were measured by real-time quantitative PCR, Western blot, and immunohistochemistry.

Results

maLPA₁-null mice exhibit an attenuated CL response after cocaine conditioning but a normal BS after repeated cocaine exposure. These behavioural changes were associated to alterations on the expression of metabotropic mGLUR3 glutamate receptors and on the actions of cocaine on the GLUR1 subunit of AMPA glutamate receptors in the hippocampus of maLPA₁ animals. Striatal dopaminergic markers (tyrosine hydroxylase, dopamine D1 receptor, and dopamine transporter DAT), were similar in both genotypes and were equally affected by cocaine exposure.

Conclusion

The present results indicate that the lack of LPA1 receptor affect cocaine-induced conditioned locomotion but not behavioural sensitization. The findings suggest that LPA1 receptor may be necessary for a normal associative contextual learning associated to cocaine, probably through the modulation of hippocampal glutamatergic circuits.     

Serotonergic modulation of social interactions in isolated male mice

Several serotonergic drugs were tested in isolation-induced aggressive behavior in male mice using ethological methodology. Eltoprazine, a mixed 5-HT₁ agonist, reduced aggression but enhanced social interest and exploration. Several 5-HT_1A agonists (8-OH-DPAT, ipsapirone, buspirone, 5-Me-ODMT) and a 5-HT uptake blocker (fluvoxamine) also reduced aggression. Although these drugs somewhat differentially affect aggressive behavior, the isolation-induced paradigm alone is not sensitive enough to successfully differentiate and screen the various serotonergic drugs with regard to their influence on social behavior in mice. It is argued that various animal paradigms in several species are necessary to describe specific effects of serotonergic drugs.     

Haloperidol catalepsy in grouped and isolated mice.

A method was worked out to assess in a quantitative and dose-dependent way the development of catalepsy of mice after low doses of haloperidol. This method was also capable of detecting the anticataleptic effect of phenytoin and the catalepsy-enhancing effect of nikethamide. After 4 weeks' isolation, the mice became aggressive and revealed increased susceptibility to the cataleptic effect of haloperidol. The analysis of the data indicates that in these experiments altered central mechanisms were more important than changes of the peripheral pharmacokinetics of haloperidol.     

Morphine action in grouped and isolated rats and mice

The present study determines the analgesic effects of morphine in grouped and isolated rats and mice. Isolated animals developed altered behavioral patterns, including mouse-killing in rats and mutual aggressiveness in mice. The analgesic effect of morphine was tested by tail compression in rats and by the hot plate for mice. Isolated rats developing mouse-killing behavior had a raised pain threshold, while indifferent animals (nonkillers) responded less to morphine. Isolated mice, particularly low aggressors, gave enhanced responses to morphine.     

Differential cocaine-induced modulation of glutamate and dopamine transporters after contingent and non-contingent administration

Although dopamine and glutamate transmission has been implicated in cocaine dependence, the effects of the extinction of cocaine self-administration on protein transporters in both of these neurotransmitter systems remain unknown. We have used a yoked-box procedure to simultaneously test rats in triads, one rat that actively self-administered cocaine (CONT), while the other two received yoked injections of either cocaine (NON-CONT) or saline (SALINE). The brains in each triad were removed and processed for quantitative autoradiography immediately after the last session of cocaine self-administration (Day 0), or after 1, 5, or 10 days of extinction, and excitatory amino acid transporters (EAATs) and dopamine transporter (DAT) binding was examined. When compared to NON-CONT and SALINE animals, binding of radioligand to EAATs was significantly lower in the hippocampal CA1 field and the cerebellar cortex of CONT rats on Day 0, although it was significantly higher after 1 day of extinction in the infralimbic cortex. No differences in EAAT binding were observed after 5 or 10 days of extinction in any of the brain regions analyzed. In contrast and at all the time points of extinction, binding to DAT was significantly enhanced in CONT animals when compared to SALINE and NON-CONT rats in different forebrain and mesencephalic regions, including the nucleus accumbens, ventral tegmental area or caudate putamen. These results suggest that changes in protein transporter binding after cocaine self-administration and extinction are transient for EAAT while they are more enduring for DAT, and that they depend on the type of access to cocaine.     

Role of the dopamine transporter in the differential cocaine-induced locomotor activation of inbred long-sleep and short-sleep mice.

The locomotor-stimulant effects of cocaine, mediated through inhibition of the dopamine transporter (DAT), can be influenced by environmental factors. Previously, we found that following a short exposure to the testing environment, cocaine induces greater locomotor activation in inbred long-sleep (ILS) mice, compared to inbred short-sleep (ISS) mice. In the present study, all animals received prolonged habituation to the testing chambers prior to cocaine injection, and the results were compared with those from our previous study. When mice were tested with saline on day 1 and with either saline or cocaine (10-20 mg/kg) on day 2, we observed significant locomotor stimulation in ILS, but not ISS, mice at all tested doses of cocaine. Thus, prolonged habituation does not alter the differential responsiveness of these two strains of mice to cocaine. We found no strain differences in striatal cocaine levels. However, [3H]WIN 35,428 binding studies showed a lower number of striatal DATs in ILS, compared to ISS, mice. In vivo analysis of striatal DAT activity revealed not only that ILS mice cleared exogenously applied DA more slowly than ISS mice, but also that cocaine (10 mg/kg) decreased DA clearance selectively in ILS mice. Thus, functional differences in striatal DATs between ILS and ISS mice likely contribute to the differential behavioral activation of cocaine in these two mouse strains.     

Bupropion effects on aggressiveness and anxiety in OF1 male mice

Rationale Bupropion is an antidepressant drug that is being used to help in giving up smoking. Its behavioral effects have been evaluated in different animal models, although limited information is available regarding its effects on aggressiveness, anxiety and exploratory behavior.Objectives Evaluate acute effects of bupropion on locomotor activity, isolation-induced aggression, hole-board and elevated plus-maze tests in OF1 male mice.Methods In the first experiment, effects of bupropion (2.5, 5, 10, 20 and 40 mg/kg) on locomotion were evaluated. In the second experiment, isolation-induced aggression was assessed in isolated male mice previously classified as short attack latency (SL) and long attack latency (LL). Mice were treated with bupropion or vehicle and confronted with standard opponents for 10 min. In experiments 3 and 4, mice were treated with bupropion or vehicle and 30 min later examined in the plus-maze or in the hole-board apparatus.Results In the actimeter, bupropion induced a dose-dependent increase in locomotion. During agonistic encounters, bupropion (10 mg/kg and 40 mg/kg) increased time devoted to attack in LL mice. In the plus-maze, no significant differences were found between bupropion-treated and vehicle-treated mice in the percentage of entries or time spent in open arms. In the hole-board, the highest dose of bupropion (40 mg/kg) significantly decreased number of head-dips and increased latency to the first head-dip.Conclusions During agonistic encounters the two sub-groups of mice (SL and LL) may display differential sensitivity in drug-induced changes on aggressiveness, since bupropion increased attack only in mice with long attack latency in the pre-screening test. In the plus-maze, this drug does not seem to have specific actions on anxiety and in the hole-board a high dose had similar effects to those induced by anxiogenic drugs.     

Opiate effects on social investigatory behavior of male mice

The effects of morphine and naloxone, alone and in combination, on social investigatory behavior and motor activity was examined in CD-1 male mice. Tests were conducted in a Plexiglas apparatus in which a center area was separated from two adjacent stimulus compartments by wire mesh screens. One compartment housed a female conspecific while the other remained empty and served as a control for non-specific investigatory responses. A photocell bisected the center compartment and recorded motor activity. Male mice were placed individually into the center area and the time spent investigating each screen was recorded using contact circuits during the 15-min test. In Experiment 1, males (N = 11) received saline, 0.1, 1.0 and 10.0 mg/kg morphine sulfate IP 20 min prior to testing. The high dose significantly decreased investigation of the female compartment while investigation of the uninhibited chamber and motor activity were not significantly affected. In a second experiment (N = 16), 3, 10 and 30 mg/kg naloxone administered 30 min prior to testing had no significant effect on any of the measures recorded. In a third group of subjects (N = 16), 3 mg/kg naloxone reversed the decrease in female investigation time observed with 10 mg/kg morphine, indicating an opiate mechanism for these results. These data provide further evidence that an animal model can be used to study the disruption of socio-sexual behavior produced by opiates.     

The effects of dopamine D-1 and D-2 receptor agonists on body temperature in male mice

The effect of dopamine D-1 and D-2 receptor stimulation on body temperature has been investigated in male mice. The selective D-2 receptor agonists, quinpirole and LY 163502, and the mixed D-1/D-2 agonist, apomorphine, induced a dose-dependent hypothermia, whereas the selective D-1 receptor agonists, SK&F 81297, SK&F 38393 and SK&F 75670, induced hyperthermia. The hyperthermic responses of these agents were of a similar magnitude although the relative efficacies determined in vitro with the adenylate cyclase assay were different. The peripherally acting D-1 agonist, fenoldopam, did not influence body temperature, indicating that the hyperthermia is mediated, centrally. Studies with combinations of quinpirole and SK&F 38393 showed that the effect of one of the substances could be counteracted by the other. Furthermore, antagonist studies showed that the hypothermia induced by quinpirole could be inhibited by the D-2-selective antagonist, YM 09151-2, and by the mixed D-1/D-2 antagonist, cis(Z)-flupentixol, but not by the D-1-selective antagonist, SCH 23390. Similar results were found for apomorphine-induced hypothermia. SK&F 38393-induced hyperthermia could be antagonized by all three antagonists. These results suggest that the two receptor subtypes act differentially on body temperature, and that they influence a common out-put system, but in opposite directions. These findings are opposite to those of behavioural studies, where a synergistic function of D-1 and D-2 receptors has been demonstrated in the regulation of motor function.     

Decreased prefrontal cortex dopamine activity following adolescent social defeat in male rats: role of dopamine D2 receptors

Rationale

Adverse social experience in adolescence causes reduced medial prefrontal cortex (mPFC) dopamine (DA) and associated behavioral deficits in early adulthood.

Objective

This study aims to determine whether mPFC DA hypofunction following social stress is specific to adolescent experience and if this results from stress-induced DA D₂ receptor activation.

Materials and methods

Male rats exposed to repeated social defeat during adolescence or adulthood had mPFC DA activity sampled 17 days later. Separate experiments used freely moving microdialysis to measure mPFC DA release in response to adolescent defeat exposure. At P40, 49 and 56 mPFC DA turnover was assessed to identify when DA activity decreased in relation to the adolescent defeat experience. Finally, nondefeated adolescent rats received repeated intra-mPFC infusions of the D₂ receptor agonist quinpirole, while another adolescent group received intra-mPFC infusions of the D₂ antagonist amisulpride before defeat exposure.

Results

Long-term decreases or increases in mPFC DA turnover were observed following adolescent or adult defeat, respectively. Adolescent defeat exposure elicits sustained increases in mPFC DA release, and DA turnover remains elevated beyond the stress experience before declining to levels below normal at P56. Activation of mPFC D₂ receptors in nondefeated adolescents decreases DA activity in a similar manner to that caused by adolescent defeat, while defeat-induced reductions in mPFC DA activity are prevented by D₂ receptor blockade.

Conclusions

Both the developing and mature PFC DA systems are vulnerable to social stress, but only adolescent defeat causes DA hypofunction. This appears to result in part from stress-induced activation of mPFC D₂ autoreceptors.     

Increased aggression and toxicity in grouped male mice treated with tranquilizing benzodiazepines

N-demethyldiazepam, diazepam and oxazepam incorporated in the diet were fed to albino Swiss male and female mice (10–50 mg per day per kg of body weight) for 6 months. Increased mortality was observed in grouped male mice but not in female or isolated male mice. Multiple skin lesions and necroses found in grouped male mice were probably due to increased aggression.     

酮康唑对可卡因致小鼠肝毒性的保护作用

目的澄清酮康唑对可卡因所致小鼠肝脏损伤具有有害的还是有益的影响。方法采用可卡因致小鼠肝损伤模型,分别使用预防性和治疗性给药两种实验方法。所有动物处死后,观察血清中谷丙转氨酶(GPT)、谷草转氨酶(GOT)、乳酸脱氢酶(LDH)的活性,测定肝脏中的还原性谷胱甘肽(GSH)和氧化性谷胱甘肽(GSSG)的含量变化和丙二醛(MDA)的含量,并进行组织病理学检测。结果单纯给予可卡因,血清中GPT,GOT和LDH活性升高,肝组织中MDA含量增加,GSH/GSSG比值下降。与单纯给予可卡因相比,预防性或治疗性给予酮康唑能够显著地降低血清中GPT,GOT和LDH活性,并且肝组织中MDA含量下降,GSH/GSSG比值回升。经过酮康唑处理后,肝脏的病理损伤程度也有明显的改善。结论酮康唑能对可卡因引起的急性肝脏损害有一定的保护作用。     

Involvement of glutamate receptors in the striatal enkephalin-induced dopamine release

In anesthetized rats, the intrastriatal infusion of the δ-opioid receptor agonist, [d-Pen²,d-Pen⁵]enkephalin, increased the extracellular concentration of dopamine. This effect was abolished by the NMDA receptor antagonist, 3-[(±)-2-carboxypiperazine-4-yl] propyl-1-phosphonate, but was unchanged by the AMPA (d,l-α-amino-3-hydroxy-5-methyl-4-isoxazole propionate) and kainate receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. This suggests that the dopamine release induced by the δ-opioid agonist depends critically on the involvement of glutamatergic transmission via NMDA receptors.     

Postnatal manganese exposure attenuates cocaine-induced locomotor activity and reduces dopamine transporters in adult male rats

In the present study, we examined whether exposing rats to manganese (Mn) during the preweanling period would affect basal or cocaine-induced locomotor activity in adulthood and reduce the number of striatal dopamine transporter binding sites. On postnatal day (PD) 1-21, rats were given oral supplements of vehicle or Mn chloride (250 or 750 microg/day). Striatal Mn and iron (Fe) accumulation as well as serum Fe levels were measured on PD 14, PD 21, and PD 90. Throughout the dosing period, rats were evaluated on standard measures of sensory and motor development. During adulthood, the basal and cocaine-induced locomotor activity of vehicle- and Mn-exposed rats was assessed using automated testing chambers. After completion of behavioral testing, striatal dopamine transporter binding sites were measured using [(3)H]GBR 12935. Results showed that early Mn exposure enhanced striatal Mn accumulation on PD 14 and PD 21, while depressing serum Fe levels on PD 21. Exposure to Mn on PD 1-21 did not affect striatal or serum Mn or Fe levels on PD 90. During the second postnatal week, Mn-exposed rat pups performed more poorly than controls on a negative geotaxis task, however basal motor activity of preweanling rat pups was not affected by Mn treatment. When tested in adulthood, basal locomotor activity of vehicle- and Mn-exposed rats also did not differ. In contrast, adult rats previously exposed to 750 microg/day Mn showed an enhanced locomotor response when challenged with 10 mg/kg cocaine. A different pattern of results occurred after treatment with a higher dose of the psychostimulant, because Mn-exposed rats showed an attenuated locomotor response when given 20 mg/kg cocaine. Importantly, Mn-exposed rats exhibited long-term reductions in striatal dopamine transporter binding sites. Considered together, these results indicate that postnatal Mn exposure has long-term behavioral and neurochemical effects that can persist into adulthood.     

Co-activation of glutamate and dopamine receptors within the nucleus accumbens is required for spatial memory consolidation in mice

Rationale The nucleus accumbens receives glutamatergic and dopaminergic inputs converging onto common dendrites. Recent behavioral data demonstrated that intra-accumbens administrations of either glutamate or dopamine (DA) antagonist impair spatial memory consolidation. Thus, also based on the biochemical and molecular findings demonstrating interactions among the different receptors subtypes for glutamate and dopamine, it is conceivable that memory consolidation within this structure might be modulated by glutamate–dopamine receptor interactions.Objectives The purpose of this study was to examine the effects of intra-accumbens co-administrations of glutamate and DA antagonists on the consolidation of spatial information.Methods On day 1, CD1 male mice were placed in an open field containing five different objects and immediately after three sessions of habituation the animals were injected intra-accumbens with either vehicle or low doses of the N-methyl-d-aspartate (NMDA; AP-5 50 ng/side), the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA; DNQX 5 ng/side), the D1 (SCH23390 12.5 ng/side) and the D2 (sulpiride 25 ng/side) antagonists that were ineffective alone in disrupting object displacement. Separate groups were then focally injected with a combination of one of the glutamate antagonists with one of the dopamine antagonists. Twenty-four hours later, the ability of mice to discriminate object displacement was assessed.Results Controls and mice injected with ineffective doses of the NMDA, the AMPA, the D1 or the D2 antagonists were always able to react to the object displacement. On the contrary, the groups administered with the different combinations (AP-5 and SCH23390, AP-5 and sulpiride, DNQX and SCH23390, DNQX and sulpiride) of glutamate and dopamine antagonists did not discriminate the spatial change.Conclusions These results demonstrate that glutamate–dopamine receptor interactions within the accumbens are essential for the consolidation process of spatial information.     

Role of genotype and dopamine receptors in behaviour of inbred mice in a forced swimming test

The role of genotype in the effects of selective D1 and D2 dopamine agonists and antagonists on behavioural despair (Porsolt's test) was studied. Mice of nine inbred strains showed significant interstrain differences in duration of immobility. The influence of dopaminergic drugs was assessed in six strains characterized by different levels of swimming activity. SKF 38393 (10 mg/kg), an agonist at D1 dopamine receptors, increased swimming activity, while the D1 antagonist SCH 23390 (0.2 and 0.5 mg/kg) reduced it, the effects being genotype dependent. The involvement of D2 dopamine receptors in the regulation of mouse behaviour in the forced swimming test was not so evident; the D2 agonist bromocriptine (10 mg/kg) produced no significant effect. The D2 agonist quinpirole (2.5 mg/kg) increased immobility in the majority of the mouse strains studied, while in CBA mice it resulted in a marked reduction of immobility. The D2 antagonist sulpiride (20 mg/kg) decreased immobility and increased active swimming only in two strains. The present results suggest a different role for D1 and D2 dopamine receptors in the regulation of swimming in the mouse.     

Effects of AMPA/kainate glutamate receptor antagonists on cocaine-induced convulsions and lethality in mice

The effects of pretreatment with protein kinase C and protein kinase A inhibitors on the intraventricular insulin-induced attenuation of the antinociceptive effect of [D-Ala2, N-MePhe4, Gly-ol5]enkephalin (DAMGO) were studied in mice. Intracerebroventricular (i.c.v.) pretreatment with insulin dose- and time-dependently attenuated the antinociceptive effect of i.c.v. DAMGO (5.6 ng) in mice. Intracerebroventricular pretreatment with a highly selective tyrosine kinase inhibitor, herbimycin A, at doses of 200 and 600 ng for 70 min, dose-dependently reversed the attenuation of the antinociceptive effect of DAMGO (5.6 ng, i.c.v.) caused by insulin. Furthermore, i.c.v. pretreatment with serine/threonin kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine hydrochloride (H7), at doses of 3-30 nmol for 60 min, dose-dependently reversed the attenuation of the antinociceptive effect of DAMGO (5.6 ng, i.c.v.) caused by insulin. Intracerebroventricular pretreatment with selective protein kinase C inhibitor, calphostin C, at doses of 1 and 3 pmol for 60 min, but not with a highly protein kinase A inhibitor, (8R, 9S, 11S)-(-)-9-hydroxy-9-n-hexyloxy-carbonyl-8-methyl-2, 3, 9, 20-tetrahydro-8, 11-epoxy-1H, 8H, 11H-2, 7b, 11a-triaqzadibenzo[a, g]cycloocta[c, d, e]-trinden-1-one (KT5720), at dose of 10 pmol for 60 min, reversed the attenuation of the antinociceptive effect of DAMGO (5.6 ng, i.c.v.) caused by insulin. These results suggest that the reduction of DAMGO-induced antinociception by insulin in mice may be, in part, due to the activation of protein kinase C followed by the activation of tyrosine kinase.